[Feature] Polyhedral nets

[tesseralis]

Support the display of polyhedral nets.

Initially, we'd just want a toggle somewhere in the Viewer that lets the user switch between the net and the polyhedron.

Considerations:

• operations should be disabled when on the net view
• probably want to display it as an svg
• the net calculation algorithm should determine a "pretty" net. i.e. one that fits the viewport, and one that keeps interesting facets of the polyhedron intact, like cupola faces.

If we're super cool, we could do a folding/unfolding animation: https://www.youtube.com/watch?v=Igf4BXkERyI

But this is actually really really hard, so it's not a priority.